1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to a variety of relatively sliding portions in machine tools and testing equipment and in which a slider is mounted slidable on a track rail with rolling elements interposed therebetween.
2. Description of the Prior Art
In conventional linear motion rolling guide units, the sealing between a track rail and a slider that slides on it is realized by end seals attached to the ends of the slider and under seals attached to the underside of the slider.
A linear motion rolling guide unit as shown in FIG. 6 has been known. FIG. 6 shows a perspective view of one example of a conventional linear motion rolling guide unit.
As shown in the figure, the linear motion rolling guide unit includes a track rail 1 having raceway grooves 9 extending longitudinally on both side wall surfaces 11 thereof, and a slider 19 slidably mounted astride on the track rail 1. The slider 19 has a casing 2, which is slidable relative to the track rail 1 and has raceway grooves 8 formed at positions facing the raceway grooves 9 on the track rail 1, a number of rolling elements 4 trapped and running between the opposing raceway grooves 8 and 9, and end caps 5 attached to the longitudinal ends of the casing 2, the longitudinal direction being the sliding direction of the casing 2. The end cap 5 has an end seal 30 for sealing between the track rail 1 and the slider 19. The end cap 5 is also provided with a grease nipple 18 for supplying lubricant to the sliding surfaces between the track rail 1 and the slider 19. To prevent the rolling elements 4 from coming off the casing 2, retainer bands 17 are provided to the casing 2 in such a way as to enclose these balls 4. Under seals 3 are arranged at the undersides of the end caps 5 and the casing 2 to seal sliding portions between the casing 2, the end caps 5 and the longitudinal side wall surfaces 11 of the track rail 1.
The slider 19 is mounted astride on the track rail 1 and freely slides on it by means of a number of rolling elements 4 that circulate along the raceway grooves 9 in the track rail 1. The rolling elements 4 that travel loaded along the raceway grooves 9 of the track rail 1 are led to direction changing passages formed in the end caps 5 and further to return passages 10 formed in the upper part of the casing 2 parallel to the raceway grooves 8. Thus, the rolling elements 4 run endlessly through endless circulating passages. In this way, the slider 19 is allowed to slide relative to the track rail 1 by the rolling elements 4 traveling loaded between the raceway grooves 8 on the slider 19 and the raceway grooves 9 on the track rail 1.
The under seal 3, though it has an advantage of being thin and simple in construction and easily manufactured, also has drawbacks that because the under seal 3 is thin, it is easily deformed by external forces and by positioning errors between it and the casing 2 and track rail 1, the casing and track rail having the raceway grooves 8, 9 respectively.
To describe in more detail, because the conventional linear motion rolling guide unit takes no countermeasures against elongation of the under seal resulting from thermal expansion, the under seal, when elongated, cannot maintain good sealing condition. That is, if the under seal is rigidly engaged with the end seals or with the end caps, the difference in thermal expansion between the under seal and the end caps or casing will cause unequal elongations in the engaged portion of the under seal and in the corresponding engaged portion of the casing and end caps, with the result that the under seals may become deformed or buckled, impairing the sealing condition.
In an under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 118317/1991, axial ends of the under seal are formed with axially extending projections and end seals are formed at their lower end surfaces with engagement holes for receiving the projections of the under seal. The under seal can be mounted easily and swiftly and prevented from coming off, simply by fitting the projections of the under seal into the engagement holes in the end seals. Dimensional errors between the projections and the engagement holes can be offset easily by elastic deformation of the projections or of elastic pieces placed at the engaged locations. This under seal apparatus, however, is not so constructed as to make the under seal bear tightly on the underside of the slider.
In another under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 121220/1991, the axial ends of the under seal are provided with two-pronged projections protruding toward the underside of the slider, the two prongs diverging in a V-shape and being elastically deformable toward each other. The slider has the axial end portions of the underside thereof formed with vertical holes, into which the two-pronged projections of the under seal are fitted, and also with through-holes that intersect the vertical holes perpendicularly and pass through the arm or wing portions of the slider so as to receive the two-pronged projections of the under seal therein. The under seal is mounted by inserting the two-pronged projections of the under seal into the vertical holes formed in the underside of the slider; and the slider is prevented from coming off by the engagement of the projections. At the same time, one of the two prongs fitted into the vertical holes is elastically deformed in the vertical holes, thereby preloading a lip portion of the under seal that is in sliding contact with the side wall surface of the guide rail. This linear motion guide bearing, however, does not consider a situation where there are dimensional errors with the insertion vertical holes and the two-pronged projections.